Evolution Thru Final~Human Evolution

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Major events in human evolution

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51/2 -7 mya Human-chimp divergence
4-5 mya Ardipithicus raidus (bipedialism and increase in brain size probably most important developments, bipedialism may have allowed hip changes that allowed babies with larger skulls to be born)
2.7-4 mya Australopiticus afarensis (Lucy 40 % complete-most complete skeleton found for a long time)
35-250 kya Homo neanderthalensis (first cousins-coexisted at the same time as Homo sapiens)
~70 kya Homo sapiens
extinct ~12 kya Homo floresiensis (recently discovered in SE asia-‘hobbits’-isolated island population, primates tend to be smaller on islands -large mammals tend to get smaller and small mammals tend to get larger on islands)

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what is the significance of Ardipithicus?

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-great insight to this stage of evolution,
-bipedialism & increase in brain size
-large number of fossils and ability to date them due to vulcanism

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human evolution phylogenetic tree

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common chimps and bonobos most closely related
most closely related to humans

that group most closely related to gorillas

that group most closely related to orangutans

gibbons outgroup for all of them

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theories of earliest human evolution;

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-oldest fossils found in Africa, alternate hypothesis proposed Middle East

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theories about how humans came into North America;

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over Bering land bridge ~15-18kya, NA at that time was in glacial max with two massive ice sheets that people came down between, Clovis points found in SW US dated ~12kya

alternative hypothesis proposes humans came into US earlier by coastal route hopscotching between ice free areas, some South American sites have been dated much older than 18kya but not sure how well that data is substantiated

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summary of key points in ardipithicus articles

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-Woodland omnivore of forest canopy and floor
-similar body size in males and females
-small canine/premolar indicates minimal social aggression
-more flexible wrists supported weight on palms when on all fours
-not chimp like
-many fossils due to high sedimentation
-date-able due to frequent vulcanism
-carbon isotope ratios indicate little intake from grassland habitats, indicates early hominid evolution was not responding to living in an open environment
-Ardipithicus had a small brain and small chewing muscles
-developments in brain orientation might be an indication of enhanced development of visual and spatial perception
-changes in Ardipithecus pelvis allowed efficient upright walking